i prefer bottom easier to work with, plus in my case a have a went right under it, so it get fresh cold air through the bottom and spits it out the back of the PSU.Edited by spice003 - 5/24/11 at 10:48am

Of course there are advantages to a top mount too. I would assume that it would help suck hot air out of the top of the case if you don't have a fan up there. That's all fine as long as your PSU isn't getting too hot I suppose.

IMO each has its pros and cons, and it also depends on the case. If the bottom has an open hole for the psu to breath on the bottom then that is a +. However, the bottom while it is easier for cables since you can just lay them there, having the PSU in the top forces me to do better cable management often resulting in looking much cleaner. It just really depends but in general I like it better in the bottom if there is a good amount of room between it and the bottom of the motherboard.